The present invention relates to ceramic composites having a special organizational structure and a process for manufacturing the same. More specifically it relates to ceramic composites having high toughness, high strength, thermal resistance and wear resistance. The present invention relates also to a process for manufacturing the same.
Al.sub.2 O.sub.3 can be easily sintered and has excellent properties such as thermal resistance, corrosion resistance and electric insulation, and has long been used widely as an industrial material. However, it has defects of possessing low strength, low fracture toughness and low thermal shock resistance. Accordingly, attempts have been made to improve these disadvantages by making composites. The R & D on manufacturing composites, however were mostly concerned with how to achieve complexing in the micron level with particles (such as TiC) or whiskers (such as SiC whisker) dispersed as a second phase. Accordingly, there is a limit to the improvement of these mechanical properties. By making composite formations using these dispersed particles or whiskers, the fracture toughness is improved by crack deflection developed because of the maldistribution of the dispersed particles in the grain boundary of Al.sub.2 O.sub.3, or the pulling of the whiskers. However, it is well known that in a grain dispersed composite, the cracks are deflected by the dispersed grains which are localized at the Al.sub.2 O.sub.3 grain boundaries, and that the fracture toughess of the resulting sintered Al.sub.2 O.sub.3 is thereby increased.
In a ceramic such as sintered Al.sub.2 O.sub.3, the matrix thereof consists of anisotropic grains. Accordingly, the localized stresses generate at the grain boundaries by the thermal expansion mismatch between the matrix and dispersion, and the localized compressive stress is accumulated during cooling down from the sintering temperature. Then, this grain boundary becomes a fracture source which decreases the strength of the whole sintering. When fine particles are dispersed in a matrix it is expected that the toughness is improved, because those particles avoid propagation of the cracks. However a prior art technology that comprises dispersing those fine particles in the matrix was by no means effective in significantly increasing the strength, because there was no change in the grain boundaries which function as the source for fractures. Thus, the strength cannot be greatly increased.